Spotlight devices that radiate specific areas by emitting light in specific directions are conventionally used in applications of supplementary lighting, ceiling lighting, showcase lighting and so on.
In recent years, however, white light emitting diodes (white LEDs) have started been used as light sources for spotlight devices from the perspectives of power consumption reduction and environment protection.
The mainstream of current white light emitting diodes employs mode using fluorescent materials, and are generally referred to as “bluish/yellowish pseudo white light emitting diodes.”
Here, FIG. 1 shows an example of such a white light emitting diode. This white light emitting diode 1 is formed by covering a plurality of light emitting elements 3 of a plurality of blue diodes, aligned on substrate 2, with YAG fluorescent material 4. Further, this white light emitting diode 1 is designed to provide white light by mixing blue light emitted from light emitting element 3 and incident on fluorescent material 4, and yellow light produced in fluorescent material 4 as fluorescence.
However, light fluxes of white light that are emitted from white light emission surface 5 of white light emitting diode 1, diverge over a wide angle from the white light (i.e., center light) emitted in the surface normal direction of emission surface 5 at an emission angle 0 (degrees), and therefore, to adopt white light emitting diode 1 in spotlight devices, a means for concentrating white light emitted from emission surface 5 in the direction of the illuminated surface, is required.
Characteristics of such white light emitting diode 1 are known that, in light fluxes emitted from emission surface 5, the white light of the center part where the emission angle from emission surface 5 is low gives bluish white light, and the white light of the peripheral parts where the emission angles from emission surface 5 are high gives yellowish white light. This is because white light emitted as blue light from light emitting element 3 at a low emission angle passes through a short optical path in fluorescent material 4 connecting light emitting elements 3 and emission surface 5, and therefore the proportion of white light mixed with yellow light during the course of fluorescent material 4 is low. Moreover, because white light emitted as blue light from light emitting element 3 at a high emission angle passes through a long optical path in fluorescent material 4 connecting light emitting elements 3 and emission surface 5, the proportion of white light mixed with yellow light during the course of fluorescent material 4 is high.
Accordingly, taking such characteristics of white light emitting diode 1 into account, in order to adopt white light emitting diode 1 in spotlight devices, a means for preventing bluish white light and yellowish white light from generating unevenness color on the illuminated surface, is required.
So far, a technique is proposed as disclosed in, for example, Patent Literature 1 that, by arranging a lens on the emitting side of white light emitting diode 1 and applying light diffusion processing to the lens forming surface provided on optical paths of yellowish white light, yellowish white light is diffused and white light emitted from the white light diode is concentrated toward the illuminated surface, and bluish white light and yellowish white light that reach the illuminated surface are mixed to prevent unevenness color (see, for example, Patent Literature 1, paragraph [0020]).